A second aqueous system we have developed for DNP relies on a trityl radical developed by NYCOMED. The trityl radical has a very narrow EPR line, is extremely stable, and can be associated with biological systems (unlike other narrow radicals, which are typically used in organic systems). Such a narrow line cannot sustain the thermal mixing effect at high field because the linewidth is less than nuclear Zeeman frequencies. However, polarization transfer to the nuclear rotating frame, rather than the lab frame, is possible with a narrow radical. This experiment (called RF-DNP) offers some potential advantages over the corresponding lab frame experiment. Polarization transfer rates may be drastically faster, and power requirements may be reduced, since the nuclear frequency has been effectively reduced. However, the shorter rotating frame relaxation time may result in a smaller final enhancement than in the lab frame. In a frozen trityl/water/glycerol solution at 10 K, we were able to achieve six times the thermal equilibrium proton polarization in less than 50 ms with irradiation from a 20 mW Gunn diode source. Because of the fast polarization growth, the experiment can be recycled at least every second, rather than the typical polarization growth characterized by Tin (which is usually tens of seconds at low temperatures).